Windows 7 - USB's ports not working properly in Win 7

Hi.
My system is Dell OptiPlex 740,‎‎ 2.50 GB RAM, Win 7 Ultimate 64bit.
All of a sudden - the USB ports (all 7 of them) stopped to function properly.
Each device I plugged into the port - got recognized as 'uknown device' and doesn't function at all.
One of the biggest problems that this cause me - I can't plug in the keyboard and the mice - I don't have PS/2 ports in this computer.
Thing is, even out of Windows, the USB doesn't work. I'm suspecting this because the PC giving me 'Keyboard fault' everytime I restart. So I can't got to BIOS either.
Right now I'm using special combination of USB hub attached to one of the ports, and the peripherals connected to the hub.

I'll be very happy to know what's the answer to my problems..

TY in advance.

Then the problem lies in your hardware or its a bug in the BIOS, consider updating your BIOS, a newer version is available
Reset the CMOS battery

Ok, but how can I update the BIOS if I can't get to it?
Pressing F2 doesn't do nothing, as expected..

Shut down your computer completely, unplug the power cord from the back for at least a minute. Then power back up.

With the power cord unplugged, press the PC's power button to completely drain the power supply, then plug it back in and power up. < saves waiting that minute or two and guaranties that its completly discharged.

Are any of the Diagnostic Lights on (in the back)?

Do you have an internal memory card reader in that rig? If so, try:

1. Disconnecting the reader inside the case, or
2. Install a memory stick in the reader before you boot.

Also try unplugging everything USB except for the keyboard.

Well, TY guys very much for the suggestions.
Will try them all and see what's working.